The present invention relates generally to a video printer and more particularly, to the tracking adjustment of a slave tape in a high-speed video printer.
One of the conventional methods of making reproduction of magnetic tapes uses a printer for magnetic tapes. This printer is constructed to print a magnetic pattern of a master tape on a copy or slave tape by directly contacting magnetic surfaces of the master and copy tapes with each other, to which heat or magnetic field is applied.
A general task to be fulfilled by the printer is to print a geometric magnetic pattern of the master tape on the copy tape as correctly as possible. In view of such task, JP-A 58-23330 proposes a technique of preventing lateral displacement between the master and copy tapes. JP-A 2-247823 proposes a technique of arranging a positioning means by which side ends of the running master and copy tapes coincide completely with each other.
When printing is carried out by only one video printer and one master video tape recorder (VTR) for recording a video signal on the master tape under restricted conditions, the above techniques proposed by JP-A 58-23330 and JP-A 2-247823 are effective. However, when printing is carried out by a plurality of video printers and master VTRs over a long period of time to produce copy tapes, a problem of compatibility between the devices becomes serious which does not arise when using only one video printer and one master VTR.
Referring to FIGS. 5A-5C, a description will be made with regard to this problem. FIG. 5A shows a format of a master tape 501, which has a video signal track 502 and control (CTL) signal 503 recorded thereon.
FIG. 5B shows a format of a slave or copy tape 511, which has a video signal track 512 and CTL signal 513 printed thereto. Reference numeral 514 designates an initial position of a reproducing head.
FIG. 5C shows the slave tape 511 displaced with respect to the master tape 501 upon printing. In case of FIG. 5C, the slave tape 511 indicated by a fully-drawn line is displaced upward with respect to the master tape 501 indicated by a dotted line.
As for reproduction of the copy tape, suppose that when a video signal track and a CTL signal are printed in the state that the master tape 501 as shown in FIG. 5A and the slave tape 511 as shown in FIG. 5B coincide completely with each other in the tape cross direction, a position of a reproducing head of a reproducing device with respect to the CTL signal is adjusted so that the initial position 514 of the reproducing head with respect to the CTL signal 513 is in the center of the video signal track 512 as shown in FIG. 5B.
If printing is carried out in the state that the slave tape 511 is displaced upward as shown in FIG. 5C, the video signal track 512 printed from the master tape 501 to the slave tape 511 has a start position near a lower edge of the slave tape 511.
Referring to FIG. 5C, upon reproduction of the slave tape 511, as being adjusted to have a predetermined height "h" from the lower edge of the slave tape 511, the reproducing head occupies a position 516 with respect to a recorded position of the CTL signal. Thus, the video signal track 512 cannot be read out by a center portion of the reproducing head, i.e. track displacement is produced.
Therefore, in order to make the reproducing head pass a center portion of the video signal track 512 and occupy a position 515 with respect to the CTL signal, the reproducing head should parallelly be moved by one in the longitudinal direction of the slave tape 511.
The same problem arises when reproduction of a tape copied from a different master tape from that one as shown in FIG. 5A is carried out by the reproducing device having a reproducing head height "h" as shown in FIG. 5B.
Therefore, with the conventional high-speed video printer, the height of guides in a tape running system should be always controlled and maintained to keep displacement between the master and slave tapes upon printing within an error of several microns.
Moreover, when using a plurality of master tapes having different CTL signal positions, the height of the guides should be adjusted every tape change, resulting in a lowering of the productivity.
As for a procedure of conventional tracking adjustment, first, a video signal recorded on the master tape is printed on the slave tape according to the above method, producing a sample tape.
Then, the sample tape is wound in a cassette. This sample cassette is set in a reference reproducing device to reproduce a video signal as recorded therein. At that time, an output signal of the reproducing device is measured by a measuring device such as an oscilloscope.
Tracking adjustment is carried out in observing a waveform of the output signal displayed on the oscilloscope. Specifically, a position of the reproducing head is adjusted so that the amplitude of a video radio frequency (RF) signal or reproduced video signal is maximum. At that time, the reproducing head occupies the position 515 as shown in FIG. 5C, so that if a video signal is reproduced from the position 515, the reproducing head can trace the center portion of the video signal track 512.
However, if displacement of a lower edge of the sample tape is greater than a predetermined value due to displacement with respect to the master tape upon printing, etc., the position 515 of the reproducing head when having the maximum video RF signal is displaced with respect to the normal tracking start position 516 as shown in FIG. 5C, producing displacement between a position of the CTL signal and a start position of the video RF signal, which corresponds to track displacement.
If track displacement is within tolerance, it is judged that this track displacement is allowable, finishing tracking adjustment to carry out mass production of the tapes. If not, the height of the guides of the video printer is changed by in the order of several microns, and the above procedure is repeatedly carried out.
The work of adjusting the amount of track displacement in the reference reproducing device by the height of the guides of the video printer is difficult, even for a skilled person, to accomplish decisively, requiring usually some additional adjustment. This results in a lowering of the productivity upon mass printing of the tape.
It is, therefore, an object of the present invention to provide a video printer which is free from the above drawback and enables easy adjustment of track displacement.